Assume 10 cu m of brickwork

1 cu m = 500 no. of bricks

10 cu m= 5000 no of bricks

Volume of one brick $= 0.19 × 0.09 ×0.09 =1.539 ×10^{-3}$

Total volume $= 5000×1.539×10^{-3}=7.695 cu m$

Dry volume of mortar $= 10-7.695 = 2.305cu m$

Wastage $= 1.2 {\times} 2.996 = 3.596 cu m$

Cement $= \dfrac{3.596}{1+4}=0.7192$

No of cement bags $= \dfrac{07192}{0.035}=20.54 ≈21 bags$

Sand $= 0.7192 {\times} 4 = 2.87 cu m$

Final Cost = Rs. 5640/ cu m